In the art of cookery the making of pastry for the upper and lower crusts of pies is an ancient skill and one practiced by almost all housewives. A mann of properly prepared dough is placed on a floured flat surface and thinned by rolling pressure applied in strokes directed radially outwardly in many directions, the mass of dough being thereby converted to an approximately circular thin sheet. With acquired skill, the cook is able to select an initial quantity of dough which can be rolled out to a crust of proper thickness and of generally circular outline slightly larger than a pie pan. The process is accomplished using a cylindrical rolling pin a few inches in diameter, and longer than the diameter of the pie pan.
The rolling of pastry crust is in fact an accelerated flow procedure, the dough acting as a plastic or extremely viscous and somewhat elastic liquid. A wide range of doughs is known, from very rich pastry doughs to self-rising and yeast doughs. Each stroke of the rolling pin causes a "wave" of dough to move outwardly ahead of the roller. A shearing force develops between the dough being moved at each end of the roller and the adjacent masses of dough, and after the crust has reached some degree of thinness these shearing forces tend to produce thin spots in the crust. A skillful cook almost unconsciously varies the pressure of the roller against the dough at different locations in the rolling stroke, and also continuously varies the radial direction of the stroke, to mitigate this problem.